A measuring machine which has a probe mounted onto a measuring head and performs various measurements by bringing the probe close to a work from any direction comprises a lifting drive device for the measuring head in many cases. Probes such as a contact/non-contact probe, a high resolution camera, and the like are selectively mounted onto the measuring head in accordance with various measurements, and a position (coordinate), an image, a shape and the like of a work are measured with high precision by respective probes. Further, measurements are sometimes performed with a lighting apparatus mounted onto the measuring head to illuminate a part to be measured of a work by the lighting apparatus.
Japanese Patent No. 3988860 (hereinafter, Patent Literature 1) discloses a Z-direction drive mechanism which is a lifting drive device for a conventional measuring head. As shown in FIG. 5, this Z-direction drive mechanism comprises a Z-axis spindle 12 having a probe 13 at an lower end and supported vertically, a guide tube 22 for guiding the Z-axis spindle 12 in a vertical direction, a support shaft 28 extending upward from the inside of the Z-axis spindle 12, a pair of rollers 15, 16 provided to the Z-axis spindle 12 and interposing a support shaft 28 therebetween, and a driving motor 17 for rotationally driving the roller 15.
The guide tube 22 is supported by an X-slider 9 of an X-direction drive mechanism and moves in X-direction. The Z-axis spindle 12 is inserted into the guide tube 22, and a plurality of air pads 24 for a plurality of air bearings is arranged in a space between the Z-axis spindle 12 and the guide tube 22. The air pad 24 is arranged in the inner periphery of the guide tube 22 and forms an air bearing by jetting air to reduce friction resistance between the guide tube 22 and the Z-axis spindle 12. Further, a post 25 standing vertically upward is provided to the guide tube 22, and a horizontal beam 26 provided at an upper end of this post 25 supports the upper end of the support shaft 28.
A piston is connected to a lower end of the support shaft 28 inserted into the inside of the Z-axis spindle 12, and a cylinder for housing this piston is provided inside the Z-axis spindle 12. By supplying air into a cylinder chamber, a floating force acts on the cylinder. This floating force becomes push-up force corresponding to the weight of the Z-axis spindle 12, so that an apparent weight of the Z-axis spindle 12 is reduced. Such mechanism is referred to as an air balance mechanism herein.
To drive the Z-direction drive mechanism of Patent Literature 1, a motor 17 is driven to rotate a driving roller 15. The driving roller 15 and a driven roller 16 interpose the support shaft 28 suspending the Z-axis spindle 12, so that the rollers 15, 16 lift while rotating by the friction force between the rollers 15, 16 and the support shaft 28. Accordingly, the Z-axis spindle 12 moves up-and-down, and the probe 13 can be set at a desired height.